The present invention is intended for use in connection with pan-tilt-zoom (PTZ) cameras. PTZ cameras and dome cameras are two of the most common camera types used in various types of surveillance applications. Both types of cameras can move in various directions, and are typically controlled by a computer system that receives input from a user using some kind of control device, such as a joystick, while viewing the captured images on a display.
Panning is defined as movement in a horizontal plane of the camera, and tilting is defined as movement in a vertical plane of the camera, respectively. There are three main types of movement models that can be used to describe how to move the camera from a first position to a second position: absolute movement, relative movement, and continuous movement. In the absolute movement model, the new position of the camera is described by a destination position in a fixed pan/tilt coordinate system (e.g., “Pan to 36.25 degrees and tilt to −20.70 degrees”). The user input is typically generated by a user entering coordinates for the new position as numbers. In the relative movement model, the new position of the camera is described as pan and tilt distance offsets from the current camera position in the a fixed pan/tilt coordinate system (e.g., “Pan left 2.50 degrees and tilt up 6.45 degrees”). The user input is typically generated by a user clicking with a mouse (or a similar pointing device) in a displayed image to select a point to which the user wishes to redirect the camera. In the continuous movement model, the new position of the camera is described as a direction and a speed (i.e., a vector) and will continue until another movement command is issued (e.g., Pan right at 10.50 degrees/second and tilt down at 5.25 degrees/second). The continuous movement model is the classical “joystick control” used by most manual operators.
A dome camera, which is typically mounted on the ceiling in a building, has unlimited pan (i.e., the dome camera can perform an unlimited number of 360-degree rotations in the pan plane), and can typically tilt 180 degrees, thereby covering a complete semi-sphere. When the dome camera tilts past nadir (i.e., the point straight below the camera), the camera will be upside down. In order to display a right-side-up image to the user, the image captured by the dome camera is automatically flipped (i.e., rotated 180 degrees).
A PTZ camera, on the other hand, typically has a pan range of +/−170 degrees (that is, less than 360 degrees total pan range), and a tilt that varies, typically from 0 to −90 degrees, or from 0 to −180 degrees. These restrictions are due to mechanical limitations caused by, for example, power and data cables that connect the maneuverable part of the PTZ camera with the stationary part of the PTZ camera. FIG. 1 shows a schematic view of a PTZ camera 100 having a stationary element 120 and a maneuverable element 130 to which a camera block 140 is attached. The stationary element 120 has a mechanical stop 110, which physically engages with a mechanical stop 150 on the maneuverable element 130 to limit the movement of the maneuverable element 130.
U.S. Pat. No. 6,392,693 describes an example of a monitoring camera that has an automatic pivoting function when the camera reaches a predetermined position. When the camera reaches the predetermined position, the camera automatically pivots to a different position which can be set by a user. The document describes an application in which the camera monitors a walkway between two doors and can be used to follow people walking from the first door to the second door. When the second door is reached, i.e., the predetermined position, the camera automatically returns to the original position where it monitors the first door. The image displayed to the user freezes during the transition from the predetermined camera position to the original position. Various embodiments also provide for enabling or disabling the automatic pivoting function. Since the monitoring camera used in this document is a PTZ camera, it suffers from the same problems that were discussed above. That is, even if the camera can cover the walkway, as described in the exemplary embodiment, the camera lacks a 360 degree continuous panning capability and a 180 degree tilting capability, which gives limited viewing abilities to the camera operator.